Sounds like grounding was a part of it, but definitely not the whole deal. Gotta be something unique about the truck units to react differently to the exciter wire.

 

I'm hearing whispers in the old threads when this first started happening, that rebuilders are using a new regulator triggered by ecu that requires another pin to the harness plug to.turn on high voltage (or a different voltage fed into it). That GM stated doing this on 07+ cars and trucks, So a truck alternator from a truck plug and harness has a different trigger than an fbody and the new rebuilt alternators have this minimum or maximum trigger that our fbodies don't have, or fbodies send incorrect voltage or resistance to the reman alternators

So the alternator rebuilders tested this design on the trucks so they could use all rebuild parts retroactively, and since the Fbody isn't a large market they never tested it's application. Where as all of the reman truck alternators when installed on a truck will still work because they made whatever design change was needed to use just one style part across the design line

Whatever the reason, only a used truck alternator, or used camaro alternator will work on an fbody because of this.

I believe it's a design change in the pin (or change in voltage to the regulator) to the rebuilt alternator or brand new alternator that makes rebuilt or new alternators fail on the fbody, and the reason why a used truck alternator will still work is that GM did not use that style regulator in alternators prior to 07. But now every rebuilder uses the new cross compatible regulator

Used truck alternator passed btw. You can also see the ripple is cut in half compared to the new 145amp store bought alternator








And compare those to 2 different brand new out of the box alternator from the other day

 

Big difference there.

I don't believe the high low thing above and here's why... If there was a high low discrepancy, the alternator would have never performed fine for that first day or two, or week, or months... it would have never triggered the high side and you would have seen low output from day one. So the description you heard doesn't necessarily add up.

The rebuilt alternators will and do put out appropriate voltage right out of the box which tells me the alternator was turned on (exciter wire fed voltage in and triggered the regulator) and the regulator took over and did it's job and it ran 14ish volts even when hot with everything on. But obviously something fails shortly after because that performance drops off. Again, if it were a "never triggers the higher output" thing, you wouldn't have had varying performance and a drop off. You'd have one consistent output/activity.

There may be something to something being used across the board or maybe a different description. Who knows, it's sad we have to deal with this and I can't imagine being someone trying to figure this out that hasn't come across this thread. Edit: Never mind I was that guy that's why I made this thread to begin with lol.

The newer vehicles that you were referencing use a load current sensor on the battery cable and vary the regulator based on load, those are the two wire alternators.

Your car looks ******* sick btw.

 

Side note to everyone, the worse the condition of the battery the harder the alternator works to keep it charged and will kill even a quality alternator. Back in my first couple of years being a tech I put 3 alternators on a mercury cougar and finally figured out the battery needed approx 30 amps of input to maintain its charge and was overworking the alternator. Less than a year ago I had a kia in here that the alternator appeared to be dead on since voltage at the battery was only 12 volts while running. I knew it needed a battery so I replaced the battery first, it charged near 14 volts after the battery change.

I did test and try that on my camaro and it didn't make a difference. The alternators were just ****, period.

 

Agreed. My alternators were all brand new gold units, used on brand new optima batteries, the first a yellow top 34-78, this one a 78 red. (My wife's car has the 34-78 yellow top because it is never driven and yellow tops are also deep cycle batteries )

The extra ground cable might have made a difference too, never tested it against a regulator test. I saw a peak voltage gain and then gradual decline, but to be fair the used truck alternator does the same thing. But I'm also only seeing voltage through an internal accessory wire. I saw the voltage dip after a few minutes and in a frenzy I pulled the alternator out of my truck

To be clear I never suffered a low voltage situation that wouldn't charge the battery, I suffered either a voltage or amperage condition that would dimly illuminate the check gauges cluster at night. My used truck alternator cured that problem. Seeing the fbody exciter diagram the check gauges light is indeed wired into the exciter wire as resistance, something that the trucks don't have. The ls1 swap guys also have different issues and have been known to just run the straight 12v exciter wire with no resistance

I drove the car like this for over a year according to my warranty file, I'm chasing a intermittent p0300 and trying to eliminate any possible situation. The voltage is my 4th process to eliminate, and the p0300 immediately disappeared with my used truck alternator. However it's not a resolved issue, as the car gets older the list of items to check gets longer

Thanks for the compliment, I get the itch to pull it apart for a bad *** build but I love being able to daily drive the car and not having to look over my shoulder about my motor. The wheels have completed the car for me, I've owned her for ten years and she has 140k miles and gets a thorough maintenance and interior overhaul ever 5 years or so. I've thought about selling her many many times, but I'm glad I didn't. Now the fbody market is all back yard motor builds or run down beat up cars.

I'm sure you're at the same point with your clean truck, if you sold it you would be starting over with a blank slate in worse condition than YOUR truck it's always better to know what you have, than it is to buy what you want

 

******* brilliant

I inspected my m6 harness extremely thoroughly, how the heck did I miss this???

The used one was doing the same as the duralast, start reading up and the 98 only has 1 pin. I'm sure they are mistaken I tell myself. Well 5 minutes later im pulling the plug and the end of the harness and find butt connectors, really, really, in an engine harness on an alternator trigger wire.

 

What's the reason someone would do that? Why does your plug have 2 wires?

 

Was able to give the junkyard alternator a good work out today. Cruised around long enough till I figured everything in the engine bay was good and heat soaked. Then headed out to a spot which would allow me to make a good pull. On the way my engine temp dropped down a little, so upon arrival at the spot I let the car idle for as long as it took to kick on fan high speed. I then manually switched on my trans cooler fan, turned the high beams on, fog lights on, a/c on and ran both Windows (3rd gen f body camaro) up and down multiple times. My voltage never dipped below 13.5. Left everything on and made two WOT hits to 100 mph. This alternator never flinched. It took less abuse than that to kill the reman units. I think my charging problem is in the rear view.

 

Not sure, engine harness was converted to a 6 speed, bought it off of Craigslist from a guy who parts out fbodies.

Most likely the 98 m6 car he was parting out had a truck or corvette pigtail from a junk yard. My front drivers 02 sensor was also just hanging in the loom with electrical tape, when I went to pull the harness up from below with everything disconnected I could feel a wiggle, the 02 sensor butt connector wires were just loose and the electrical tape was kind of holding them in place

So in the end I believe I solved my random p0300 and my alternator issue. Also explains why adding in a ground cable to the alternator case was giving me strange voltage kick downs, or just messing with that harness shook those butt connectors enough to cause problems

I would swap back to the 145 amp alternator but I'm sick of seeing my alternator.

I kept my original a4 harness in my attic for this exact reason. Can never have enough spares.

 

Yeah that should definitely only be one wire, and it should go to the L terminal on the alternator. Even my 00 was only a one wire, they all were.

I agree about selling and starting over, and it reminds me I should have kept the SS. I had countless hours in it in details, much less the mods, and it was modded to be a really fun daily. It was my personal daily 6 flags, and even though it didn't have a cam, it frequently pulled cammed cars. Just had a really well laid out setup.

 

Bad ***, kinda sad but it's an awesome feeling being able to know you can hammer on it again without getting stranded over something as stupid as an alternator.

 

Took the car to work today. Morning drive was uneventful. 14v with the lights on. Coming home the Guage was dancing around between 12v and 13.5v. It was also flickering with the turn signals which is completely new. By the time I got home it did stabilize at 13.5 ish. Don't know what to think now except maybe a new exciter plug.

 

Ordered a new exciter plug and a used kg3 from LKQ online. I'm not 100% sure what alternator I have now because it came from ebay and had a 130A stamp on it. It's still kinda working so I'll carry it around as a spare. I'm sure I could roadside one off and on in 10 minutes. Hopefully the new exciter plug and an actual kg3 takes care of this ****. My next recourse would be to put the resistor inline on the exciter wire. But I was under the impression that it was unnecessary on ecm controlled exciters. Who knows. Sucks driving around staring at the damn V gauge.

 

Damn that sucks, keep us posted. Are you using this in an F Body? If so no changes are needed to the exciter.

Are you in Texas? Possibly close to Dallas?

 

Swapped third gen f body. Donor car was a 2000 f body. I'm in Pennsylvania.

 

Gotcha. I'm in Dallas and have my original OEM alternator sitting here is why I asked.

 

I did the swat in 2015, forgot which alt I used, but regardless, I'm still having charging issues. First off I have a slow drain coming from somewhere. If I don't drive the car for about 3 days, the battery is dead, and it's a new Interstate battery.

As for the charging issues, there are days that my gauge reads 13+, however, most of the time it's read well below 13. Like the other day, it was so low, that I was getting performance issues, like the Bird had no *****... at one point I thought it was going to stall out.

I'm wondering if it's my grounding, or bad alt, but if not, what else could it be?

 

Under 13 is not normal and points to an alternator failure.

 

thanks for the thought. Took the car out yesterday and it charged fine, but did continue the flicker with the turn signals which I don't get. I'm still going to install the kg3 and see what happens. I'm going to start carrying a spare alt around so I don't have to worry about getting stranded.

 

Not sure but here's one thing I'd like to point out, nobody that has gone the used alternator route has reported any issues (actually I think maybe one person). Many (most) that used a new one, truck or f body, have had problems. So all I can tell everyone is don't start looking at the car and everything on it until you have a known good alternator and the most dependable replacements so far are used truck alternators.

Sucks to hear that. Hope that kg3 comes in soon and takes care of all the trouble. I still remember how aggravating it all was.